In Patent Document 1, the technology disclosed is a remaining capacity indicator of a lead-acid battery for an electronic motor vehicle that obtains a discharge rate at each measurement time point on the basis of an internal resistivity defined and calculated based on a measurement of an internal resistance executed in completing full charge and in a temporary stop while a vehicle is moving and corrects a calculated value of a remaining capacity by a current integration method, wherein the remaining capacity indicator is constituted of each unit of a measuring unit connected by a cable, a display circuit unit, and a display LED unit. The measuring unit has an analog circuit portion and a digital circuit portion. The analog circuit portion has an internal resistance detecting unit comprising a forced discharge circuit by a resistor and a differentiating circuit to detect a voltage drop and a current change in a forced discharge.